1. Field of Invention
This invention is generally related to controlling the depth of a laser cut by adjusting the beam size and/or the energy density or power of a laser.
2. Description of Related Art
Making a connection between two fluid containing or transporting components is widely practiced. In the new and emerging area of microfluidics, the fluid carrying components are small, in the range of 500 microns down to as small as 1 micron and possibly even smaller. For a general description of this class of devices, see for example, the conference proceedings xe2x80x9cMicrofluidic Devices and Systems,xe2x80x9d Proceedings of the SPIE, Vol. 3515 (1998).
Microfluidic devices pose challenges in fluid path connection both within the microscopic componentry and also for the connection between a microfluidic device and macroscopic fluid containers or transporters. Such microfluidic devices are important in a wide range of applications that include drug delivery, analytical chemistry, microchemical reactors and synthesis, genetic engineering, and marking technologies including a range of ink jet technologies including thermal ink jet printing.
In existing thermal ink jet printers, such as disclosed in U.S. Pat. No. 4,774,530, the print cartridge comprises one or more ink filled channels, each communicating with a relatively small ink supply chamber or manifold, at one end and having an opening at the opposite end, referred to as a nozzle. In each of the channels, a thermal energy generator, usually a resistor, is located at a predetermined distance from the nozzle. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble, which expels an ink droplet.
U.S. Pat. No. 5,736,998 describes an improved ink seal between a nozzle plate and the pen cartridge in an ink jet printhead. Though mention is made of optimized shape and the use of a dispensed bead of adhesive, no mention is made of a laser cut seal or a discreet fluid seal member.
Previously, a typical end-user product in this art was a cartridge in the form of a prepackaged, usually disposable, item comprising a sealed container holding a supply of ink, and a die module having a linear or matrix array of channels operatively attached to the sealed container. Presently, however, products are designed using a more permanent (or at least multi-use) print cartridge connected to a replaceable ink tank unit.
However, in many of the various print cartridge designs, an important feature of the print cartridge is the fluid seal which is generally located between the ink supply manifold and the ink drop ejecting die module. The fluid seal is important because it must ensure a tight seal between the ink manifold and the die module. If a tight seal is not maintained, then ink can leak out of the print cartridge through the connection area and/or air and other contaminants can be introduced into the print cartridge and ink supply. A second important function is to seal the ink manifold fluid path in areas adjacent to the die module.
One example of a fluid seal is disclosed in U.S. Pat. No. 5,696,546, which describes an ink cartridge for an ink jet printer having an ink supply in a housing in fluid communication with an ink supply manifold. The ink is contained in an absorbent material in the ink supply, which has a housing floor having a vent and an ink outlet into a manifold. The manifold is an elongated recess in the outer surface of the housing. There can be a single or multiple chambers connected to a single or multiple ink supplies, depending in part on whether the print cartridge is a monochrome or multicolor print cartridge. The one or more chambers in the manifold have a common flat surface. A fluid seal or film member is bonded to this flat surface by an adhesive not attacked or eroded by the ink. This bond between the fluid seal and manifold must prevent ink from leaking from the manifold or ink leaking between chambers within the manifold.
There is at least one via or opening that goes all the way through the fluid seal for each chamber in the manifold. These vias provide fluid communication between each manifold chamber and an inlet of the die module. The surface of the film member opposite the surface bonded to the manifold is coated with a thermosetting adhesive, which bonds to a die module surface containing the ink inlets. The die module ink inlet is of similar size and is aligned with the vias in the fluid seal. The adhesive makes a seal around the via in the fluid seal and the inlet to the die module to provide a fluid communication path between a chamber of the manifold and the inlet to the die module while preventing fluid from leaking out of the desired fluid path. The adhesive bonding the fluid seal to the housing floor is either a pressure sensitive adhesive or the same thermosetting adhesive that is used on the other side of the film member. In the 546 patent, the fluid seal is cut using a die cutting method.
Die cutting sheet stock containing one or more thick layers of adhesive can leave adhesive on the cutting tool and cause additional distortion, failure to meet dimensional tolerances or jamming of the die cutting tool. To reduce sticking or to delay its onset, lubricants are frequently used to coat the die-cutting tool. Though the lubricant can be effective in this job, the lubricant can also modify or contaminate the adhesive so that it does not perform as well as an uncontaminated adhesive.
The die cutting process also involves shearing action between two cutters. The shearing action can create plastic fibers and adhesive strings. A large plastic fibers can create a leak path if it is located between the adhesive and sealing surface. Smaller plastic fibers can be carried by ink into the die module and clog the fine jets in the die module or otherwise impede ink flow into or through the die module. The adhesive strings can create difficulties in handling the fluid seal in the assembly equipment for the print cartridge or migrate to the surface of the die module containing the ink exit nozzles and interfere with the operation of the printing.
In forming the fluid seal for inclusion in a manufacturing line for automated assembly of print cartridges, it is convenient to have the fluid seal remain on a carrier tape. This can be done by not cutting through one layer, such as the bottom layer, of a multi-layered sheet stock. To cut partially through the sheet stock requires good control of the cut depth. Since the adhesive layers can re-flow, it is important to separate the adhesive on opposite sides of the cut. The shearing action of die cutting can cut through the adhesive layers but, since it does not remove material, the parted adhesive has a tendency to reflow and stick back together. When this happens, the part may be difficult to remove on the manufacturing line or strings of adhesive can interfere with the assembly process.
The complications and shortcomings inherent in die cutting of fluid seals are significant design limitations on an ink jet print cartridge containing fluid seals. The complications in the creation of parts with die cutting leads to significant problems with part yield and with loss of fully assembled print cartridges. Design limitations, process limitations, and both part and print cartridge yield all lead to a significant cost associated with the die cutting process.
Laser cutting and ablation methods are generally known, and have been applied in various methods within the ink jet art, as well as in other arts. U. S. Pat. No. 4,049,945 describes a method for cutting different shapes in a moving web by using both the motion of the web and the linear scanning of the laser to be able to cut individual features rather than using step and repeat and encompasses only scanned spot cutting. U.S. Pat. No. 4,639,572 describes cutting composite materials, such as circuit boards, that contain a filler and a polymer matrix and is not directed to multilayer sheet stock. U.S. Pat. No. 5,630,308 describes a method for scoring packaging material using a laser such that the scored line is weakened enough to enable controlled tearing of the material. A process for cutting through several members while leaving one member intact is not described. U.S. Pat. No. 4,549,063 describes using a laser to make discontinuous cuts to provide perforations in an adhesive laminate. The perforations permit tearing labels off a laminate backing.
Laser cutting methods are also known in the art for forming large parts. For example, laser patterning and cutting methods have been used in many areas, such as sheet metal fabrication, cloth cutting, and paper cutting.
Laser ablation has been used in the ink jet art to form specific features in ink jet die modules, such as ink passageways, orifices, and the like. U.S. Pat. No. 5,208,604 describes an ink jet head, where the ink discharge opening is formed by laser ablation, i.e., by irradiating an excimer laser onto the discharge opening plate. Similarly, U.S. Pat. Nos. 5,312,517 and 5,442,384 disclose forming specific features in an ink jet head using laser ablation methods. However, in each of these patents, none of the cuts form a sealed fluid path between two segments of the print cartridge, and the bulk part itself is cut using traditional cutting methods, while the laser is used only for forming features such as holes, lines, and the like.
Using of a laser to cut material involves control of a number of process parameters, including, for example, the material thickness, the laser beam width or diameter, the laser beam power, the laser beam energy density, the scanning speed or dwell time for a CW (continuous wave) laser, and/or the number of pulses for a pulsed beam. Cutting all of the way through the material using a laser allows for a relatively large latitude in the process parameters. The relatively large latitude is possible as the interaction of the laser beam with the material ends once the through cut is completed.
It is more difficult, however, to form a cut to a controlled depth, or a xe2x80x9ckissxe2x80x9d cut. The difficulty arises from the fact that the laser beam is in contact with the material for the duration of the cutting process. Cuts to a controlled depth are frequently formed in a linear region of the process parameters. In other words, the cut depth is proportional to the process parameters. For example, the cut depth is proportional to the dwell time or scanning speed when cutting with a CW laser. As another example, the cut depth is proportional to the number of pulses when cutting with a pulsed laser beam.
Linear process parameters are convenient when the thickness of the material to be cut is changed or when changing the dwell time of the laser beam, for example, by adjusting the scanned cutting speed. Working in the linear range of the process parameters also allows for high cutting rates and rapid processing. The linear range of the process parameters can also be used for controlled depth cuts when the parameters are tightly controlled and non-varying and/or when the thickness of the material to be cut is very well controlled.
It may not be possible to control the process parameters and/or the thickness of the material to be cut to achieve a controlled depth cut to a satisfactory level of accuracy. If control of the process parameters and/or material to be cut is possible, it may be very expensive, however, to control the process parameters and/or the thickness of the material to be cut to achieve a controlled depth cut to a satisfactory level of accuracy. For example, if the laser power varies by 2% and the material thickness varies by 2%, in order to form a controlled depth cut to within three standard deviations, or for example, 3% of the thickness of the material, a closed loop control is necessary to control the laser if the cutting is being done in the linear range of the process parameters. In some cases, closed-loop control alone is insufficient to insure the repeatability of the desired cut depth. In this case, the nonlinear behavior of this invention facilitates controlled-depth cuts with high reliability.
This invention provides systems and methods for controlling the depth of cuts by a laser. As generally practiced in the art, fluid seals and other parts are cut from multilayer sheet stock using a die cutting process. For an application such as the creation of fluid seals, the shortcomings of die cutting include large design rules, both distortion of the adhesive or other layers near cut edges and long range distortion, the use of lubricants, generation of debris, and difficulty in making controlled-depth cuts.
In various exemplary embodiments of the system and method according to the invention, cuts of controlled depth are formed by a laser beam into a continuous web of sheet stock that includes a plurality of layers. The systems and methods according to the invention enable the creation of parts that remain on the continuous web by cutting the sheet stock to a controlled depth. The controlled depth cutting permits creation of a shape or part in several layers of the sheet stock and makes it possible to not cut through at least one of the layers of the sheet stock that forms the continuous web. The depth of the cutting is controlled by adjusting at least one of the laser beam width and the laser power. The laser beam width and/or the laser power is adjusted so that a high linear cutting rate is initially established and a lower, non-linear cutting rate is developed later in the cutting process at a depth that is near the desired final cut depth.
The non-linear cutting rate is achieved by varying the cutting beam width or diameter and/or the laser beam power or energy density. Adjusting the cutting beam width or diameter and/or the laser beam power or energy density so that the cutting rate is non-linear allows for rapid processing of cuts to a controlled depth and a large latitude in the laser beam width or diameter and/or the laser beam power or energy density.